There are numerous medical procedures that involve the administration of relatively large volumes of liquid to a patient. Where such liquids are administered intravenously, it is essential that bubble-free sterile liquids be fed to the patient in controllable rates and quantities. The term "liquid management system" is used herein to denote various means for connecting a patient to a liquid source. One illustrative example of a liquid management system is an apparatus including a spike, tubing, valves, needle, etc., for establishing a liquid flow from a source to a patient for intravenous administration of an imaging liquid for angiography.
For many reasons, hospitals are becoming more aware of a need to reduce costs. One way in which savings may be achieved is by the conservation of medical intravenous liquids. As an example of such liquids, angiography procedures require the use of contrast media. These contrast media are radiopaque liquids that image vasculature.
In the past one container of liquid (contrast media) would typically be used for each procedure. After the procedure, the container was disposed of even if it was not empty. This wasteful procedure was required because of the danger of patient-to-patient contamination with the multiple use of a single container. That danger was present because of the bi-directional route of liquid flow between patient and container. The danger of patient-to-patient contamination can be avoided by eliminating the bi-directional flow, e.g., with a one-way valve, and disposing of any portion of the liquid management system that may have been in liquid communication with a previous patient's body fluids, e.g., everything downstream of and including the one-way valve.
To manage the flow of liquid to a patient, e.g., the quantity and rate of flow, various flow regulator devices have been incorporated into liquid management systems, for example, a burette. A burette can be filled with a desired amount of liquid, e.g., the quantity needed for a planned procedure. However, liquid flow through a burette may present several problems.
First, dropping liquid through an air-space into the base of a burette may lead to bubbling. Second, a relatively large amount of liquid must always be present in a burette, usually greater than 20 cc, in order to minimize the occurrence of bubbles. This requirement is due to several factors. A primary one is that if the level of liquid is too low, a drop containing a bubble may have enough momentum from its fall to tunnel through the liquid and enter the downstream tubing with the bubble intact. Another important factor is that the increased pressure at the base of a large amount of liquid tends to drive any bubbles towards the surface of the liquid, thus removing them from the base where the liquid enters the downstream tubing. An additional factor is that drawing larger quantities of liquid from a burette accidentally may cause the burette to become depleted of liquid, thus starting an undesirable intake of air into the tubing leading to the syringe. Third, filling a burette may increase the set-up time for a liquid management system significantly. Fourth, an operator must manually observe the liquid level in a burette and refill the burette periodically in order to prevent the liquid level from being depleted.